T. Yamamura, H. Nakamura, Shunpei Nakajima
Dec 1, 1998
Citations
0
Influential Citations
3
Citations
Journal
Inorganica Chimica Acta
Abstract
Abstract Reaction of Boc-Glu-Thr-Ile-His-OMe (Boc: butoxy carbonyl) (H 2 1 ), and Zn(ClO 4 ) 2 ·6H 2 O in N,N -dimethylformamide (DMF) was studied using NMR and mass spectrometry with respect to the active sites of proteases. The study of H 2 1/Zn 2+ = 1:1 mixture in DMF-d 7 revealed that Zn 2+ is bound to the His-imidazolyl group. The results of IR experiments on the 1:1 dried material suggested that the Glucarboxyl group still remains in the form of -COOH. Mass spectrometry showed that Zn 2+ in H 2 1 /Zn 2+ attracts water molecules under the ionization conditions of fast atom bombardment. The temperature ( T ) dependence of 1 H NMR of H 2 1 /Zn 2+ = 1:1 in DMF-d 7 , studied in the temperature range 218–323 K, revealed that the Zn 2+ unit undergoes protonation and hydration at low temperatures (below 253 K). The chemical shifts ( δ ) of the amide protons were nevertheless linearly dependent on temperature over the range 218–323 K, meaning that the 1:1 solution obeys the common reaction equilibrium and that the averaged main-chain folding of the peptide moiety is conserved. Based on this finding, the distance geometry and restrained molecular dynamics analyses were carried out using the distance information on 61 1 H— 1 H pairs, extracted from the rotating frame nuclear Overhauser effect spectroscopy experiment on this solution (300 K). These analyses revealed that the averaged main-chain folding of the Glu-Thr-Ile-His is just superimposed on that of the Zn 2+ binding sites of proteases forming a single helix with the Glu carboxyl group situated in the vicinity of the His imidazole group, or is directly but distally bound to Zn 2+ (in the case of γ-COO Glu − ). The hydrogen bond between γ-COO Glu − and the H 2 O on Zn 2+ was also found in comparatively higher energy area. Gel chromatography of the dried material obtained from H 2 1 /Zn 2+ = 1:1 mixture gave only [(H 1 ) 2 Zn] ( 2 ), as a discrete compound. The coordination atoms to Zn 2+ in 2 were assigned as Glu amide (N − ) and His imidazole nitrogens.